Power amplifiers are categorized into several classes. Class-D power amplifiers are switched-mode amplifiers that are sometimes used to amplify a Pulse-Width-Modulated (PWM) input to generate a Radio-Frequency (RF) output that is phase modulated. Very high switching speeds may be used.
Unfortunately, even and odd harmonics are often generated above the fundamental frequency. These harmonics are undesirable as they can violate emission limits set by regulatory agencies such as the U.S. Federal Communications Commission (FCC).
High power transmitters require high power amplifiers that use large transistors. These large transistors switch large currents that are slow to change. Thus rise and fall times or edges of signals are slow and consume a relatively large portion of the period in a high frequency signal. Rising and falling edges may mismatch significantly. Distortions that are thought to create harmonic distortions may be caused by rising and falling edge mismatch, and duty-cycle mismatch when the rising and falling times cause the duty cycle to deviate from 50%.
What is desired is a switch-mode power amplifier with reduced harmonics. A power amplifier with harmonic suppression is desirable. A circuit that can suppress harmonics created by a power amplifier is desired.